Building on previous work by Broyles, et al. (2003), and Feuerstein, et al. (2005), which address the existence of local “tornado alleys”, local severe (F3+) tornado alleys are quantitatively identified across the United States by local maxima of high frequency and density of violent tornadoes (see attached Figure). Further, the tornadic environments of these regions are described and intercompared over a 30 year period (1979-2009) using atmospheric composites from CFS reanalysis.

Through this intercomparison, statistically significant differences in thermodynamic and dynamic conditions of the environments of each subregion were identified. These include surface-based CAPE, 0-3km storm-relative helicity, lapse rates and vertical wind shear over various layers. Additionally, the composite mean synoptic patterns for each subregion are analyzed and intercompared to elucidate differences in the pre-tornadic synoptic and mesoscale forcing mechanisms.

The noteworthy tornado outbreak over the Southeast United States on 26-27 April is examined as an independent case study to compare the event to the typical environment for severe outbreaks in this region. The second goal of this work is to determine if this event occurred within the confines of the pre-defined severe tornado alleys (see attached Figure) and, moreover, to examine how its dynamic and thermodynamic forcing differs from regional climatology defined above.